Analysis of the advantages of single chip microcomputer in power supply design application

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Analysis of the advantages of single chip microcomputer in power supply design application [Copy link]

Power supply designers often face conflicting requirements. On the one hand, they need to reduce size and cost, and on the other hand, they need to provide more functions and increase output power. Due to the limitation of principle, the functions of analog power supply itself are limited, and the design of analog power supply controller is becoming more and more complicated. For this reason, some designers turn to pure digital power supply design. However, for many designers, it is not easy to turn to unfamiliar fields so quickly. A more feasible compromise is to use traditional analog power supply, but add a digital microcontroller as the front end.

The advantage of this design is that the control of the power supply itself is still implemented using analog technology. Therefore, the power supply designer can add new functions to an existing design without having to start all over again with a digital design. With this approach, the design still uses the familiar error amplifier, current sensing, and voltage sensing circuits. Of course, although some design elements (such as the compensation network) are still implemented using discrete components, the rest is controlled by the microcontroller.
The functions that the microcontroller can provide can be divided into four categories: control, monitoring, diagnostic functions, and communication. We will discuss these functions in detail below. The first type of control function is related to the hardware interface between the microcontroller and the power supply. In analog design, it is very important to leave an interface for connecting to the microcontroller. Some power supply controllers generate control signals (such as reference voltages) internally. Such controllers provide few external connection points for the microcontroller. Microchip's MCP1630 power supply controller is designed to provide a rich connection point for the microcontroller. For this article, we assume that the power supply controller provides two control points-a shutdown input and the ability to set the reference voltage.

Although these two connection points may not seem like much, they can provide very powerful control functions and complex functions. Currently, the role of microcontrollers in many power supply designs is mainly monitoring. Many microcontrollers have on-chip analog-to-digital converters (ADCs) and analog comparators. Therefore, microcontrollers are ideal for monitoring signals such as input voltage, input current, output voltage, output voltage, and temperature. The ability of microcontrollers to monitor such a wide range of signals allows them to perform more functions, such as intelligent fault detection.

The versatility of the microcontroller comes from its programmability, which can be easily customized to meet design requirements. In this way, fault conditions can be classified and handled. Brief overcurrent and other non-critical faults may only require setting a flag. Faults such as overheating may require shutting down the power supply until the fault is corrected. Faults that require restarting the power supply can also be more strictly controlled. If there are too many faults in a certain period of time, the microcontroller can permanently shut down the power supply.

The processing power of the microcontroller also enables complex computational measurements, such as real-time calculation of power. Determining power values in analog systems requires complex analog calculations. But for a microcontroller, this is a piece of cake. Parameters such as input power, output power, efficiency, and power loss can all be calculated. Finally, the monitoring capabilities of the microcontroller can also support more advanced functions, such as fault prediction. By comparing the operating current in real time with historical data, the power supply designer can determine the conditions that lead to power supply failure.

The ability of the power supply to predict its own failures can save costs and provide greater reliability. Monitoring data is not just for fault detection. Many other actions can be taken based on the data. These tasks fall into the category of decision functions. Decision functions allow power supply designers to add greater flexibility, functionality, and protection to their designs. Let's consider the case of soft start or undervoltage lockout. Using a microcontroller to perform these tasks, the lockout voltage and soft start ramp rate are programmable and do not rely on analog devices. Decision functions can also perform more complex tasks. For example, power-up sequencing.

A power supply can be programmed to monitor another voltage and not start until the monitored voltage reaches a set value. There may also be situations where two voltages must rise in proportion or follow each other. All of these functions can be implemented by simply modifying the software without making any changes to the hardware. Another possible application of the deterministic function is to adjust the current limit based on temperature. This allows the power supply designer to use the temperature derating parameters of the device to ensure reliable operation. The deterministic function can also be used to compensate the device, thereby improving its accuracy.

Many data sheets give how parameters vary with temperature. In this case, a microcontroller can be used to implement temperature compensation. This allows designers to use lower-cost components and compensate the results based on temperature. Microchip application note AN1001 (DS01001) describes how to achieve ±0.1°C temperature sensing accuracy using a ±6°C temperature sensor through compensation. The microcontroller's diagnostic capabilities can also be used to self-calibrate a power supply so that it provides a known voltage at the output, which is detected and stored by a voltage feedback circuit.

In this way, any error in the voltage feedback resistors is eliminated, allowing the use of low-cost resistors without sacrificing accuracy. Furthermore, the hardware for both the 5V and 3.3V supplies is identical, only the calibration process is different. These are just a few examples of how the microcontroller's diagnostic functions can be used. They are only given to show the power of microcontrollers. As you can see, a large number of power supply parameters can be monitored and controlled by a small and inexpensive microcontroller. But we haven't discussed the storage and retrieval of information yet. This is where power supply communication becomes important. There are many ways to communicate with power supplies, from the simplest jumper or switch settings to complex protocols such as Ethernet.

Simple communication methods can be used to set parameters such as output voltage or operating mode. More complex protocols can support more complex and comprehensive control and monitoring of the power supply. The real value lies in remote communication. This is extremely important for telecom and server power supplies located in remote areas. This remote monitoring capability also allows operators to improve system reliability. In addition, remote communication allows operators to adjust voltage and current limits based on expected load conditions. At the same time, using redundant power supplies can further improve reliability and uptime. Once the power supply receives a signal indicating that a fault has occurred, it can notify the operator, shut down the failed power supply and activate the backup power supply. This process can also be automated, and the failed power supply can be automatically activated and switched to the backup power supply according to set conditions.

Power supply communication is not just for monitoring and setting operating parameters. Many microcontrollers have on-chip EEPROM to store data such as production information. In the event of a device failure, the equipment operator can easily determine which power supplies are affected. At the same time, maintenance history can also be stored. This ensures that the power supply's production data, maintenance history, and operating information are always at hand and kept up to date. There is currently a common misunderstanding about the rich tasks that can be achieved using microcontrollers listed above.

Designers may think that these tasks must be accomplished using a high-end microcontroller or digital signal processor. In fact, all of the tasks described in this article can be easily implemented using a low-cost 8-bit microcontroller. In addition, this design using a microcontroller is not intended to replace existing analog functions, but rather to complement the analog system, providing the entire power system with the flexibility and processing power that only a digital microcontroller can provide.

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At present, many power products are configured with MCU and controlled by power IC.

This allows for greater flexibility.